Orthohantaviruses in Misiones Province, Northeastern Argentina

Few cases of hantavirus pulmonary syndrome have been reported in northeastern Argentina. However, neighboring areas show a higher incidence, suggesting underreporting. We evaluated the presence of antibodies against orthohantavirus in small rodents throughout Misiones province. Infected Akodon affinis montensis and Oligoryzomys nigripes native rodents were found in protected areas of Misiones.

Since 2003, <10 orthohantavirus cases have been diagnosed in Misiones (4,5).However, the circulation of >1 pathogenic genotype and the presence of 3 known orthohantavirus reservoirs, together with a higher incidence of human cases in neighboring states of Brazil, suggest that HCPS might be underreported in this province (2,3,6).Underreporting is likely a result of the high rates of poverty, rurality, and lack of access to healthcare in Misiones (7,8), factors that are known to contribute to underreporting of diseases (9).To identify areas with a potential for higher risk for HCPS, identifying areas where pathogenic orthohantavirus circulates within the rodent community is crucial.In this study, we sought to estimate the seroprevalence of orthohantavirus (as a proxy for infection) and identify the main hosts in protected areas of Misiones.This research was reviewed and approved by the institutional animal care and use committee of the University of Buenos Aires (Faculty of Natural and Exact Sciences).

The Study
We conducted 24 trapping sessions spanning 2-4 consecutive nights in 10 protected areas throughout Misiones Province: Iguazú National Park and Urugua-í Provincial Park in the north; Cruce Caballero, Piñalito, Caá Yarí, and Moconá provincial parks and Forestal Belga protected area in the central part of the province; and Osununú Natural Reserve, Campo San Juan Federal Park, and De las Sierras Provincial Park in the south (Figure 1).We live-trapped rodents during October 2019-February 2023.In each area, we set 60-200 Sherman traps, plus 90 cage traps in some areas, along tracks in the woods.We baited Sherman traps using a mixture of peanut butter, fat, and rolled oats (plus bananas and sardines in most trapping sessions), whereas we baited cage traps with chicken meat and carrots.We identified captured animals up to the last taxonomic level possible according to external morphology.We recorded sex and reproductive conditions of individual rodents.We obtained a blood sample from a small cut on the tip of the tail and later used that sample to analyze the presence of antibodies against orthohantaviruses by using ELI-SA (10).To estimate the diversity of the small rodent community in each study area, we calculated richness, Shannon-Wiener diversity index (−Σp i × ln (p i ), where p i is the relative proportion of species i in the community), evenness (H/H max , where H max = ln[S]), and Simpson diversity index (1 − Σp i 2 ) using the overall data per trapping area.
We detected antibodies against orthohantavirus in A. aff.montensis mice with an overall seroprevalence of 0.007; overall seroprevalence in Oligoryzomys sp.rodents was 0.083 (Table 2).Seropositive rodents were captured in 4 natural areas, Urugua-í, Cruce Caballero, Iguazú, and Forestal Belga; Urugua-í was the only area in which antibodies were found in both species (Table 2; Figure 1).Because of its relevance to this research, the seropositive Oligoryzomys sp.rodent captured in Iguazú National Park was identified at the species level through molecular characterization.We amplified a fragment of the cytochrome b gene (1073 bp) by PCR using primers Mus 14095 and Mus 15398 (11).We used BLAST (http://blast.ncbi.nlm.nih.gov) to compare the sequence obtained (GenBank accession no.PP372564) with reference GenBank sequences and identified it as O. nigripes (98.71%BLAST identity and 100% coverage).
All seropositive rodents were active males (the sex of 1 seropositive Oligoryzomys sp.rodent was not recorded).Overall male-to-female ratio by species was 1.7:1 for A. aff.montensis and 2.3:1 for Oligoryzomys sp.

Conclusions
Our findings not only expand the known distribution of orthohantavirus in Misiones, Argentina, but also provide evidence of orthohantavirus infection in O. nigripes rodents in the north of this province, suggesting the presence of a pathogenic genotype in an area without known human cases.This information is relevant, particularly considering that Iguazú National Park, where 1 seropositive O. nigripes rat was captured, is visited by >1 million tourists every year.
Several pathogenic orthohantavirus have been associated with O. nigripes rodents and other Oligoryzomys spp.rodents in eastern Paraguay, southern Brazil, and northeastern Argentina (1,2,12), suggesting the seropositive animals detected in this study are probably hosts of a pathogenic genotype.However, the possibility of a spillover event from infected A. aff.montensis mice cannot be ruled out because this species is an orthohantavirus host in north Misiones (3).In fact, Oligoryzomys spp.rodents and A. aff.montensis mice were found in sympatry in all but 2 areas, suggesting the high potential for genetic reassortment and host-switching events (13), particularly in Urugua-í, where both species were found seropositive.Future studies should aim to identify the orthohantavirus genotypes in these hosts.
Although the male-to-female ratio was close to 2:1 for both species, the fact that all seropositive rodents were reproductively active males supports the role of sex in orthohantavirus transmission (1,3,14).Seroprevalence in A. aff.montensis mice was positively correlated with richness.However, that evidence is weak because of the low number of sites with seropositive rodents and was not supported by any other diversity measure.
The low overall seroprevalence detected in this study suggests HCPS risk is low in Misiones Province.However, the capacity of cricetid populations to peak unexpectedly under certain conditions (14,15), in addition to the evidence of orthohantavirus circulation in northern and central Misiones, highlight the potential risk and the need to continue surveillance.

Figure 2 .
Figure 2. Orthohantavirus seroprevalence in Akodon affinis montensis mice (green dots) and in Oligoryzomys sp.rodents (blue crosses) as a function of richness and Shannon-Wiener, evenness, and Simpson indices in study of orthohantavirus in Misiones Province, northeastern Argentina.Mouse icons indicate presence of seropositive A. aff.montensis (in blue) and Oligoryzomys sp.(in orange) rodents.

Table 1 .
Number of captures per species and values of diversity indices in each trapping session and for each area in study of orthohantavirus in Misiones Province, northeastern Argentina* 1456 Emerging Infectious Diseases • www.cdc.gov/eid• Vol. 30, No. 7, July 2024 *Am, Akodon affinis montensis; Bi, Brucepattersonius iheringi; D, Simpson

Table 2 .
Number of trap nights, total captures (xcluding same-session recaptures) and seroprevalence of orthohantavirus in Akodon affinis montensis and Oligoryzomys sp.rodents in each trapping session and overall in each study area in study of orthohantavirus in Misiones Province, northeastern Argentina *Both cage and Sherman traps were used in this trapping session (more Sherman traps than cage traps).